1. Field of the Invention
The present invention relates to optical aberration measurement and correction, and, more particularly, to a system and method for achieving an empirical optimization of an objective measurement and correction of an optical system such as the human eye.
2. Description of Related Art
Optical systems having a real image focus can receive collimated light and focus it at a point. Such optical systems can be found in nature, e.g., human and animal eyes, or can be manmade, e.g., laboratory systems, guidance systems, and the like. In either case, aberrations in the optical system can affect the system""s performance.
A perfect or ideal human eye diffusely reflects an impinging light beam from its retina through optics of the eye, which includes a lens and a cornea. For such an ideal eye in a relaxed state, i.e., not accommodating to provide near-field focus, reflected light exits the eye as a sequence of plane waves. However, a real eye typically has aberrations that cause deformation or distortion of reflected light waves exiting the eye. An aberrated eye diffusely reflects an impinging light beam from its retina through its lens and cornea as a sequence of distorted wavefronts.
It is known in the art to perform laser correction of focusing deficiencies by photorefractive keratectomy (PRK), which modifies corneal curvature, and LASIK surgery. Such methods typically employ a 193-nm excimer laser to ablate corneal tissue. Munnerlyn et al. (J. Cataract Refract Surg. 14(1), 46-52, 1988) have presented equations for determining a specific volume of tissue to be removed to achieve a desired refractive correction. Frey (U.S. Pat. No. 5,849,006) teaches a method of using a small-spot laser to remove a desired volume of tissue for effecting a desired refractive correction.
It is an object of the present invention to provide a system and method for optimizing an ablative correction to a human cornea.
It is a further object to provide such a system and method that accounts for corneal anisotropy.
It is another object to provide such a system and method that includes a radially dependent attenuation of the ablation power.
It is an additional object to provide such a system and method utilizing a mathematical description that can readily be adapted into an ablation algorithm.
These and other objects are achieved by the present invention, an optical correction system for correcting visual defects of an eye. The system comprises a wavefront analyzer responsive to a wavefront emanating from an eye for determining an optical path difference between a reference wave and the wavefront. The system further comprises a converter for providing an optical correction based on the path difference and on a radially dependent ablation efficiency. The efficiency correction uses a compensating polynomial of the form A+Bxcfx81+Cxcfx812+Dxcfx813+ . . . +Xxcfx81n, where xcfx81 is a normalized radius that is optical zone specific and is measured from a central portion of the cornea, reaching a value of 1 at the edge of the optical correction zone.
A laser beam is directed to the cornea that has power sufficient for ablating corneal material. The optical correction is achieved by the removal of a selected amount of the corneal material to create a desired corneal shape change based on the optical correction.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.